Re: [PATCH 2/2] mm: thp: kill the bogus ->def_flags check in hugepage_madvise()

[Hugh Dickins <hughd@google.com>]

On Wed, 22 Jan 2014, Oleg Nesterov wrote:

> hugepage_madvise() checks "mm->def_flags & VM_NOHUGEPAGE" but
> this can be never true, currently mm->def_flags can only have
> VM_LOCKED.

But line 1087 of arch/s390/mm/pgtable.c says
	mm->def_flags |= VM_NOHUGEPAGE;
from 3eabaee998c787e7e1565574821652548f7fc003
"KVM: s390: allow sie enablement for multi-threaded programs".

Hugh

> 
> And otoh we might want to add VM_NOHUGEPAGE into ->def_flags
> but override it in vma->vm_flags via madvise(MADV_HUGEPAGE).
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
>  mm/huge_memory.c |    2 --
>  1 files changed, 0 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index bccd5a6..e8b656c 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1941,8 +1941,6 @@ int hugepage_madvise(struct vm_area_struct *vma,
>  		 */
>  		if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
>  			return -EINVAL;
> -		if (mm->def_flags & VM_NOHUGEPAGE)
> -			return -EINVAL;
>  		*vm_flags &= ~VM_NOHUGEPAGE;
>  		*vm_flags |= VM_HUGEPAGE;
>  		/*
> -- 
> 1.5.5.1
> 
> 
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